A book i dont know the title of?

I rembr I found this book in the junior section of my library and was fiction. The main character was a girl and there was also i think a black cat in the book too that had some significance. The book started off in the present time but then she went back into the time of the plague and found out what it was really like back then. It was kind of like a ghost story. The front cover of the book was scary lookin and was mostly blue and grayish with a picture of the streets during the plague and night with the dead cart going down the street in the haze. Thats all i can rembr about the book cuz i never really finished it. i hope somebody can help me out.